How VFDs save energy & money?

VFD is for controlling the speed of a motor which is under load, by changing the frequency of applied voltage. When your production line needs the motor to produce lower power, with the same torque it had before, its speed should be lowered by decreasing the frequency of applied voltage, this makes the impedance of the motor decrease and in turn, the amount of applied voltage comes lower and power consumption comes lower.

Mechanical systems utilize motors to push air or liquids through the system and good design practices require the motor horsepower to be sufficient to support the "worst case" conditions. In reality these "worst case" may seldom or never be seen in the actual system once implemented. Application of variable frequency drive allows the motor to be slowed so only the energy required to perform the work is consumed, which is accomplished by rectifying the incoming voltage and then inverting to create a different, usually lower frequency than the electrical power system normally operates at. Since the power consumed by such motors is related to the frequency squared, the savings can be large and your plant can operate at optimum efficiency.

VFD is help to reduce the power consumption and saving the life time of motor and other related parts of the pump. basically vfd is control the motor speed and its give command to the motor as a demand.